Techniques for marine geophysical surveying include seismic surveying and electromagnetic surveying, in which geophysical data may be collected from below the Earth's surface. Marine geophysical surveying has applications in mineral and energy exploration and production and may be used to help identify locations of hydrocarbon-bearing formations. Certain types of marine geophysical surveying, including seismic and electromagnetic surveying, may include using a survey vessel to tow an energy source at selected depths—typically above the seafloor—in a body of water. The energy source can emit energy, for example, seismic or electromagnetic energy, into the body of water that interacts with subterranean formations below the water bottom. Sensors may be used to detect changes in the energy field due to the interaction with the subterranean formation and generate response signals that can be used to infer certain properties of the subsurface formation, such as structure, mineral composition and fluid content, thereby providing information useful in the recovery of hydrocarbons.
In conventional systems, the sensors may be located in marine data acquisition nodes positioned directly on the water bottom. However, positioning the marine data acquisition node directly on the water bottom may have disadvantages. One such disadvantage may be that the acquired geophysical data may be affected by local variations of resistivity and/or acoustic impedance. For example, stones, bottom structures, and/or varying bathymetry may cause local variations of resistivity and/or acoustic impedance. Another disadvantage that may arise for marine data acquisition nodes positioned directly on the seafloor may be the housing containing the electrodes used for recording an electromagnetic field. The housing and electrodes may protrude from the marine data acquisition node and may bend, for example, due to unsuitable positioning of the marine data acquisition node, which may produce errors in the acquired geophysical data. Yet, another disadvantage that may arise for marine data acquisition nodes positioned directly on the seafloor may be that an acquisition node may get stuck in a bottom structure and/or among stones, which may affect the measured geophysical data.